Customizing the Billing Address checkbox style

I'm working on styling the checkout page for a 2.0 store (http://terra-nullius.co/new-homepage) and having a heck of a time changing the style of the "use a different billing address" checkbox. I've been successful with the "save password" checkbox at step 5 (which is exactly what I want to do to this one), but this one seems to be generated via js/ajax, so I can't override the style via JS.

First off that's a great looking site and an awesome implementation of FoxyCart!

The two checkboxes should be generated in the same way - set within the templates. The issue you're running into is that the active class you're utilising for the "save my password" checkbox isn't added to the "use different billing address" checkbox. The rest of your styling is applying - just not the active state.

Another approach you could take would be to use the :checked CSS selector to only apply styling when the checkbox is checked. You could also alter the template so that the billing address checkbox does include an active class.